JP, A, 2006-103654 describes an airbag for restraining an occupant in the event of a vehicle collision or the like, in which a concave portion is formed in the vertical direction on the airbag surface facing the occupant when the airbag is in an inflated state. Paragraph 0039 of the above prior art discloses that, in the event of a frontal collision, the shoulder portion of the occupant is restrained by a shoulder restraining portion located on both sides of the above-described concave portion of the inflated airbag, causing the head portion of the occupant to be restrained as it enters the concave portion.
Further, in this airbag, as shown in FIG. 4, the depth of the concave portion is shallowest in the vertical intermediate part, and gradually deepens upward and downward from this intermediate part.